# 6.5.3. Vertex-fitting convenience functions¶

Hint

A vertex fit will most likely change the kinematic properties of the decay head (mother) and, if the option daughtersUpdate (kFit) or updateAllDaughters (treeFit) is turned on, also of the daughter particles. To store the quantities prior to the vertex fit and be able to write them out to a ntuple for further analysis it is recommended to run variablesToExtraInfo before the vertex fit.

vertex.TagV(list_name, MCassociation='', confidenceLevel=0.0, trackFindingType='standard_PXD', constraintType='IP', askMCInfo=False, reqPXDHits=0, maskName='', fitAlgorithm='Rave', useTruthInFit=False, useRollBack=False, path=None)[source]

For each Particle in the given Breco ParticleList: perform the fit of tag side using the track list from the RestOfEvent dataobject save the MC Btag in case of signal MC

Parameters
• list_name (str) – name of the input Breco ParticleList

• MCassociation (str) – use standard MC association or the internal one

• confidenceLevel (float) – minimum value of the ConfidenceLevel to accept the fit. 0 selects CL > 0

• constraintType (str) –

choose the constraint used in the fit. Can be set to

• noConstraint;

• IP: default, tag B constrained to be on the IP;

• tube: tube along the tag B line of flight, only for fully reconstructed signal B;

• boost: long tube along the boost direction;

• (breco): deprecated, but similar to tube;

• trackFindingType (str) –

choose how to look for tag tracks. Can be set to

• standard: all tracks except from Kshorts;

• standard_PXD: default, same as above but consider only tracks with at least 1 PXD hit.

If the fit fails, attempt again with the standard option;

• fitAlgorithm (str) – Fitter used for the tag vertex fit: Rave (default) or KFit

• askMCInfo (bool) – True when requesting MC Information from the tracks performing the vertex fit

• reqPXDHits (int) – minimum N PXD hits for a track (default is 0)

• useTruthInFit (bool) – True when the tag vertex fit is performed with the true momentum and position of the tracks (default is false). The variable TagVFitTruthStatus is set to 1 if the truth-matching succeeds and 2 otherwise.

• useRollBack (bool) – True when the tag vertex fit is performed with position of tracks rolled back to position of the mother B (default is false). The variable TagVRollBackStatus is set to 1 if the truth-matching succeeds and 2 otherwise.

• path (basf2.Path) – modules are added to this path

Warning

Note that the useFitAlgorithm (str) parameter is deprecated and replaced by constraintType (str) and trackFindingType (str)

Warning

The trackFindingType singleTrack and singleTrack_PXD are broken and cannot be used any more.

vertex.fitPseudo(list_name, path)[source]

Add a pseudo “vertex fit” which adds a covariance matrix from the combination of the four-vectors of the daughters. This is similar to BaBar’s “Add4” function. It is commonly used for $$\pi^0\to\gamma\gamma$$ reconstruction where a vertex fit is not possible.

Here is the basic usage:

from modularAnalysis import fitPseudo
from stdPi0s import stdPi0s
stdPi0s("eff40_May2020", path=mypath)
fitPseudo("pi0:eff40_May2020", path=mypath)

Parameters
• list_name (str) – the name of the list to add the covariance matrix to

• path (basf2.Path) – modules are added to this path

vertex.fitVertex(list_name, conf_level, decay_string='', fitter='KFit', fit_type='vertex', constraint='', massConstraint=[], daughtersUpdate=False, smearing=0, path=None)[source]

Perform the specified fit for each Particle in the given ParticleList.

Info:

Direct use of fitVertex is not recommended unless you know what you are doing. If you’re unsure, you probably want to use treeFit or kFit.

Parameters
• list_name (str) – name of the input ParticleList

• conf_level (float) – minimum value of the confidence level to accept the fit. Setting this parameter to -1 selects all particle candidates. The value of 0 rejects the particle candidates with failed fit.

• decay_string (str) – select particles used for the vertex fit

• fitter (str) – Rave or KFit

• fit_type (str) – type of the kinematic fit (valid options are vertex/massvertex/mass/fourC/massfourC)

• constraint (str) – add additional constraint to the fit (valid options are empty string/ipprofile/iptube/mother)

• massConstraint (list(int) or list(str)) – list of PDG ids or Names of the particles which are mass-constrained Please do not mix PDG id and particle names in massConstraint list (valid only for massfourC).

• daughtersUpdate (bool) – make copy of the daughters and update them after the vertex fit

• smearing (float) – IP tube width is smeared by this value (cm). meaningful only with ‘KFit/vertex/iptube’ option.

• path (basf2.Path) – modules are added to this path

vertex.kFit(list_name, conf_level, fit_type='vertex', constraint='', daughtersUpdate=False, decay_string='', massConstraint=[], smearing=0, path=None)[source]

Perform KFit for each Particle in the given ParticleList.

Parameters
• list_name (str) – name of the input ParticleList

• conf_level (float) – minimum value of the confidence level to accept the fit Setting this parameter to -1 selects all particle candidates. The value of 0 rejects particle candidates with a failed fit.

• fit_type (str) –

type of the kinematic fit. Valid options are

• mass for a mass-constrained fit

• vertex for a vertex fit

• massvertex for a vertex fit with a mass constraint on the mother particle

• fourC for a vertex fit in which the mother particle’s four-momentum is constrained to the beam four-momentum

• massfourC for a vertex fit with a 4-momentum constraint and mass constraints on the specified daughter particles

• constraint (str) – add an additional constraint to the fit (valid options are ipprofile or iptube)

• massConstraint (list(int) or list(str)) – list of PDG ids or Names of the particles which are mass-constrained Please do not mix PDG id and particle names in massConstraint list (valid only for massfourC).

• daughtersUpdate (bool) – make copy of the daughters and update them after the KFit

• decay_string (str) – select particles used for the KFit

• smearing (float) – IP tube width is smeared by this value (cm). meaningful only with ‘iptube’ constraint.

• path (basf2.Path) – modules are added to this path

vertex.raveFit(list_name, conf_level, fit_type='vertex', decay_string='', constraint='', daughtersUpdate=False, path=None, silence_warning=False)[source]

Performs a vertex fit using RAVE for each Particle in the given ParticleList.

Warning

RAVE is deprecated since it is not maintained. Whilst we will not remove RAVE, it is not recommended for analysis use, other than benchmarking or legacy studies. Instead, we recommend Tree Fitter (vertex.treeFit) or vertex.kFit.

Parameters
• list_name (str) – name of the input ParticleList

• conf_level (float) – minimum value of the confidence level to accept the fit. Setting this parameter to -1 selects all particle candidates. The value of 0 rejects the particle candidates with failed fit.

• fit_type (str) –

type of the RAVE vertex fit.Valid options are

• mass for a mass-constrained fit (the 7x7 error matrix of the mother particle has to be defined)

• vertex for a vertex fit without any mass constraint

• massvertex for a mass-constrained vertex fit

• decay_string (str) – select particles used for the vertex fit

• constraint (str) – add additional constraint to the fit (valid options are ipprofile or iptube).

• daughtersUpdate (bool) – make copy of the daughters and update them after the Rave vertex fit

• path (basf2.Path) – modules are added to this path

• silence_warning (bool) – silence the warning advertising TreeFitter use

vertex.treeFit(list_name, conf_level=0.001, massConstraint=[], ipConstraint=False, updateAllDaughters=False, customOriginConstraint=False, customOriginVertex=[0.001, 0, 0.0116], customOriginCovariance=[0.0048, 0, 0, 0, 0.003567, 0, 0, 0, 0.04], path=None)[source]

Perform a Tree Fitter fit for each Particle in the given ParticleList.

Example

An example of usage for the decay chain $$B^0\to\pi^+\pi^-\pi^0$$ is the following:

reconstructDecay('pi0:A -> gamma:pi0 gamma:pi0', '0.130 < InvM < 0.14', path=mypath)
reconstructDecay('B0:treefit -> pi+:my pi-:my pi0:A ', '', path=mypath)
treeFit('B0:treefit', ipConstraint=True, path=mypath)

Parameters
• list_name (str) – name of the input ParticleList

• conf_level (float) – minimum value of the confidence level to accept the fit. Setting this parameter to -1 selects all particle candidates. The value of 0 rejects the particle candidates with failed fit.

• massConstraint (list(int) or list(str)) – list of PDG ids or Names of the particles which are mass-constrained Please do not mix PDG id and particle names in massConstraint list.

• ipConstraint (bool) – constrain head production vertex to IP (x-y-z) constraint

• customOriginConstraint (bool) – use a custom origin vertex as the production vertex of your particle. This is useful when fitting D*/D without wanting to fit a B but constraining the process to be B-decay-like.

• customOriginVertex (list(float)) – 3d vector of the vertex coordinates you want to use as custom origin. Default numbers are taken for B-mesons

• customOriginCovariance (list(float)) – 3x3 covariance matrix for the custom vertex (type: vector). Default numbers extracted from generator distribution width of B-mesons.

• updateAllDaughters (bool) – if true the entire tree will be updated with the fitted values for momenta and vertex position. Otherwise only the momenta of the head of the tree will be updated, however for all daughters we also update the vertex position with the fit results as this would otherwise be set to {0, 0, 0} contact us if this causes any hardship/confusion.

• path (basf2.Path) – modules are added to this path